Hemerythrin is the oxygen-carrying protein of certain marine worms. The kinetics of substitution by anions in oxyhemerythrin and methemerythrin will be studied over a wide range of anion and proton concentrations. Conventional and stopped-flow spectro-photometry will be used to monitor the rates of these reactions. It is hoped that the results, compared with simple iron (III) complexes, will give information on the coordination environment of irons in the protein. The chemical reactivity of the monomeric form will be compared with that of the octamer, and an attempt will be made to measure the dynamics of the octameric, monomeric equilibrium which exists with hemerythrin compounds. Finally the system offers an opportunity to investigate the rates of electron transfer between metalloproteins (iron(II) and iron(III) forms) which do not contain a heme center.